Optical monitoring of photodissolution kinetics in amorphous As-S films

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Abstract
The kinetics of the photodissolution of silver into amorphous As-S films of various compositions in the range As40S60 to As20SB0 has been investigated by monitoring the changes that occur in their reflectivity during the photodissolution process. It was found that as the S content was increased above 60at.% the rate of photodissolution increased to a maximum at around As33S67 and then decreased, the maximum rate being approximately double that for As20S80. This is attributed to the fact that only compositions within a few at.% of As33S67 yield a homogeneous material when photodoped; compositions outside this range yield a photodoped product with a phase-separated structure which may impede the passage of electrons through the photodoped layer. The effect of using silver-copper alloys as the metal source instead of pure silver has also been investigated and was found to increase the photodissolution rate by up to 12%. The photodissolution rate and the form of the time dependence of the process were also found to be dependent on the thickness of the silver layer used as the ion source. Thin silver films yield a slower rate and a diffusion-limited process whereas thick films yield a faster rate and a reaction-limited process.

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